EXHAUST EMISSION CONTROL METHOD AND EXHAUST EMISSION CONTROL SYSTEM

PROBLEM TO BE SOLVED: To provide an exhaust emission control method and an exhaust emission control system, capable of avoiding exhaust pressure rise by excessive trapping of PM and deterioration of fuel economy resulted from the excessive trapping, and preventing thermal runaway caused by an excessive accumulation of PM (particulate matter) and welding loss of DPF (diesel particulate filter) by the thermal runaway by accurately determining a forced regeneration timing even in a case in which long-time operation is performed in a low-rotating operation state where exhaust air flow rate is so small that PM accumulation is difficult to estimate based on a back-to-front differential pressure of a filter. SOLUTION: In the exhaust emission control system 1 for performing forced regeneration control by determining the forced regeneration starting timing of a DPF 12b from the back-to-front differential pressure ΔPm of the DPF 12b, when it is detected that the operating state of an internal combustion engine 10 is in a low-rotating operation state, the continuation time tm of the low-rotating operation state is measured, and when the measured continuation time tm exceeds a predetermined determination time tc, the forced regeneration control of the PDF 12b is performed regardless of the back-to-front differential pressure ΔPm of the DPF 12b. COPYRIGHT: (C)2008,JPO&INPIT